Navigational devices and methods are used for a number of applications. One class of navigational devices determines a location by determining a position relative to one or more transmitters. For instance, a device can trilaterate its position by determining the distance from each of three or more transmitters. The intersection of the distances determines the position. Various other position determination methods can also be used.
Ideally, a navigational device would be available in all or most locations that the device is to be used, use existing transmitter systems and be accurate enough for the intended application. Two prominent transmitter systems are global-positioning-system (GPS) and long range navigation (LORAN). Both GPS and LORAN offer coverage over large areas and are relatively accurate; however, neither works particularly well in locations that tend to block the transmitter signal, such as indoors or in urban environments. Thus, GPS and LORAN are not-particularly well suited for such locations.
Indoor navigational applications have a number of potential uses, such as inventory tracking, location specific customization and location related security measures. Accordingly, there is a need for navigational devices that can function in indoor and urban locations using existing systems.
These and other issues have presented challenges to the implementation and design of navigation systems, including those involving indoor location determinations and similar applications.